1. Field of the Invention
This invention relates to sound recognition. The invention detects and identifies the nature of particular sound patterns in noisy environments. In a preferred embodiment the invention is utilized as an early warning-system to alert vehicles operators of the presence of emergency vehicles which emit audio warning signals of a particular pattern. The concept that furnishes the background of the invention requires a closer look to how we view a traffic system.
On the physical level a traffic system is a network of roads, moving vehicles and pedestrians, all subject to changing conditions. The motion of vehicles and pedestrians along the roads is controlled by a set of regulations that constrain their motion, thus giving rise to an ordered state of affairs. Occasionally the ordered state is destroyed and a transition to a disordered state occurs. This could be due to unexpected changes in the road conditions which depend on the nature of the roads, the weather conditions, the functioning state of the traffic light systems, the presence of accidents, the appearance of emergency vehicles such as Police or Ambulance, and/or unexpected changes in the drivers conditions that depend on their state of awareness and their vehicle level of performance. The changes in the road and/or drivers conditions happen randomly and therefore are unexpected and that is due to lack of information. Usually drivers cannot predict with certainty what other drivers are expected to do, and so they drive almost independently of one another but of course all drive to some degree under constrain. The same applies to the road conditions. Thus a traffic system is a complex structure, made up of interacting subsystems that involve deterministic as well as stochastic processes.
The deterministic processes are of mechanistic nature which controls the traffic motion thus giving rise to order which is the normal traffic state and that is manifested by the traffic regulations and monitors. On the other hand the stochastic processes are of chaotic nature which destroys order hence increasing the accidents rate and that is manifested by the lack of information present in the traffic system.
Enhancing the level of safety in a traffic system i.e. to lower the accidents rate requires suppression of the degree of disorder which implies raising the level of information among the various interacting subsystems. To accomplish this drivers should be informed ahead of time of situations to be, of particular road or zone conditions that will be encountered, to prepare to change their course of motion regarding speed and/or direction. Practically in some situations road signs and light signals can achieve that goal but in other situations to be mentioned subsequently, these methods cannot do any help.
Most drivers response to sudden changes in normal traffic situations is limited by the driver's state of awareness that mainly depends on the vision and hearing abilities, the speed in making decisions which is drastically slowed down in states of panic or drowsiness, the ability of the car to respond to manouvers induced by the driver to avoid a certain circumstance. Generally, statistics indicate that time intervals involved in sudden changes in normal traffic situations are relatively smaller than the average driver's response time. The Police, Ambulance, Fire-Engine (PAF) vehicles emitting their siren sound is an example of informing drivers to change their course of motion by slowing down and deviating to one side of the road thus giving way to the PAF vehicle. Such a state of affairs should take place in an ordered fashion otherwise one should expect accidents and taking in consideration that PAFs drive relatively fast giving rise to a `rush` situation. Now, what happens if one or more driver fails to identify the siren sound on time and/or fails to specify the right direction of approach ? such a driver(s) will give rise to a sudden change in the traffic situation when surprised by a PAF and his response becomes unpredictable.
Statistics indicate that such drivers exist since CAR-PAF accidents occupy a significant fraction of traffic accidents. A large part of that fraction is due to the facts mentioned above. The reasons behind these facts could be attributed to:
(1) Drivers state of awareness drivers with low state of awareness mainly belong to: PA0 (2) Drivers driving habits PA0 (3) Drivers vehicles conditions: PA0 (4) Road/weather/area conditions: PA0 (a) to identify abnormal sounds at unattended or even attended areas or places as inside homes, offices, factories, trains, airplanes . . . etc., like electric sparks sounds which can be detected and identified when the device is placed near multiple-outlet power strips, high voltage power supplies . . . etc. Also it can detect sounds produced by gas leakage which may give rise to explosions, in this case the device acts as a watchman. PA0 (b) to identify irregular sounds in car engines and/or the brake-system, or any other machine, in that case it acts as a diagnostic device. PA0 (c) to identify sonic and ultrasonic sounds emitted by Fish/Birds Schools or Sea Mammals in lakes, seas and oceans and their direction of motion. PA0 (d) to identify sounds emitted by engines such as propulsion or jet engines, submarines etc. PA0 (e) to identify sounds emitted by the breaking of glass in houses or cars break-ins, in this case it acts as a watchdog; PA0 (f) to control the condition of a traffic light signal at an intersection. Once the invention identifies the siren sound it will produce a signal to swap the traffic lights in accordance to the direction of approach of the emergency vehicle relative to the intersection; PA0 (g) a multipurpose device can be built to serve most of the above mentioned purposes.
the class of people with hearing disability or hearing impairment in general; PA1 the class of elderly people that usually have less concentration on the road dynamics of change; PA1 the class of non-experienced people as the first time on the road drivers who are favorable to a panic state of mind when they experience all of a sudden situation on the road; PA1 the class of people that abuse alcohol and drugs; PA1 the class of people that reach a fatigue state from long distance driving as for instance commercial truck drivers; PA1 having the habit of listening to loud music while driving as the case with most teenagers drivers thus screening external sounds as the PAF siren sound; PA1 having the habit of talking with others or getting indulged in some other sort of activity that would distract their attention; PA1 all the situations could be aggravated if the cars are provided with sound proof windows as the case with modern ones that are usually closed in winter and in summer to maintain the air conditioning on. PA1 internal sounds like sounds generated by heating-fan system and/or the the windshield wipers that would screen external sounds; PA1 driving in noisy areas could screens significant sounds as that of the siren; PA1 echo or sound reflection effects of the siren sound usually causes confusion in deciding the right direction of approach; PA1 driving in stormy weather. The sound produced by thunder storms and heavy rain, plus that of the wipers, give rise to noisy background that would severly attenuate the siren sound, not to mention snow storms that affects the acoustics properties of the air and the ever-present broad-band wind noise.
The inability to detect the sound of a PAF vehicle due to any of the above mentioned factors may result in fatal or serious injuries as the case when a PAF vehicle attempts to cross redlights assuming that the other cars are aware of its presence, and another car is speeding to cross the greenlight unaware of the presence of the PAF vehicle. There are more cases to mention.
Also the inability to specify the direction of approach of a PAF siren results in serious accidents as the case when a driver identifies the siren sound but assumes the wrong direction of approach of a PAF vehicle suddenly finds the PAF in an unexpected site obliged by law to give way to the PAF vehicle and in a state of panic could take sudden moves causing other cars behind him to crash in a chain of collisions or simply colliding with the PAF or other nearby cars. On the other hand, even the minor effects of such accidents may cause delay of an Ambulance or failure of a Police vehicle to accomplish its duties on time. When the number of combined factors render it difficult to recognize the PAF siren sound and/or determine its direction of approach using our natural perceptions then it becomes inevitable to have an early warning system that can reliablely aid the vehicles operators by alarming them and getting their attention in time thus eliminating the element of surprise. The presented invention actually solves these problems.
2. Description of Prior Art
Efforts at providing devices for alerting vehicles operators of the presence of emergency vehicles have been taught in the past. In fact, several patents have disclosed techniques employing non-audio sensing means that detect radio signals emitted by radio transmitters located in the emergency vehicle and receivers located in the other vehicles or in traffic lights. Such sensing means are expensive and require the installation of more than a device. For example U.S. Pat. Nos. 3,233,217; 3,673,560; 3,710,313; 3,760,349; and 3,412,317.
Other patents adopted the use of a bank of filters and threshold detectors for the detection of specific signals and that has been known for more than three decades. The drawback of such a technique is that the hardware is built and tuned for the recognition of one sound pattern, based only on its frequency characteristics. The performance of the patents based on that technique with regard to the rate of false alarm or rate of miss deteriorates in the presence of noise. An example of these devices is depicted in U.S. Pat. No. 4,212,085 in which the bank of filters consists simply of one high band pass filter followed by a level detector. The direction of the incoming vehicle is determined by using three of such circuits connected to three microphone elements. The direction is then indicated by either the LED of highest brightness or by using a comparative logic. In such simple technique no attempt is made to use the specific features of the siren sounds, hence any audio signal of strong frequency component in the frequency range of the high bandpass filter, such as an automobile horn, can produce a false detection.
A similar approach is also described by Warren in the U.S. Pat. No. 4,587,522, where the output of a bandpass filter is squared and used to drive a pulse counter. A timer means is then used to provide an alarm signal if the pulse count rate falls within a specified range. This technique has better performance than the preceding one with respect to the background noise since a squarer circuit tends to emphasize the time-domain signal peaks over the background noise level. However the technique can not still differentiate between signals having frequency components within the bandpass filter. Moreover, the squaring signal tends to spread the frequency components of the signal, a signal having two strong frequency components, say w1 and w2, will have the same effect as a signal at w1+w2 and w1-w2, or 2w1 and 2w2. It is clear from the above discussion that the described patents are not reliable warning systems for two main reasons. First, the siren sound does not have a narrow frequency band, but sweeps a rather wide frequency range. For example, the audio characteristic of the sirens "yelp" mode consists of a continuously changing audio tone that begins at a frequency as low as 500 Hz and sweeps to a frequency as high as 1600 Hz and then sweeps back down again to the starting low frequency. The sweep cycle is repeated at a rate between 5 to 4 cycles per second. The exact frequency range covered and exact cycles repetition rate depends on the particular type of siren. Other siren operating modes known as "wail" and "high-low" have different audio characteristics. The second reason is that most street noises have a complex frequency spectrum that contains many audio components of different frequencies and these noises would cause almost constant false triggering, rendering the device useless, as for instance electric horns on automobiles, air horns on trucks, the screetching of brakes, the squealing of tires, engine exhaust noise, tramway or train whistles and the ever present broad-band wind noise.
An improved technique is described by Jensen in the U.S. Pat. No. 4,625,206. Unlike the previous ones, it utilizes information based on the siren sound frequency features, specifically the "yelp" mode. The circuit comprises a bank of bandpass filters and a plurality of timing and logic circuits to detect the presence of frequency components in the incoming signal that match that of the "yelp" siren sound according to a specific timing and sequence. The circuit represents a significant improvement over the other patents. The timing circuits are chosen to match an average "yelp" sound. Jensen technique utilizes only the frequency-time envelope characteristics for sound pattern discrimination. Hence can be used for detection of signals with constant amplitude-time envelope. Signals with the same frequency-time envelope but with different frequency-amplitude-time characteristics can not in general be discriminated using the above mentioned technique due to Jensen. The Jensen patent aims at controlling traffic lights. A serious drawback of this approach is the possibility of changing the traffic lights at near by intersection inspite of the fact that the emergency vehicle may not be heading towards that intersection. Strong reflections of sounds inside high rise metropolitan areas can cause wrong detection of the direction of approach of the emergency vehicle, and cause serious chaos at the intersection. It is more safer to install the receivers inside the motor vehicles where operators may perform second verification and exercise extra precaution. Moreover in many cities traffic lights are concurrently synchronized and controlled by a central computer to optimize the traffic waves across the city, overridding and perturbing the operation of such synchronized systems can cause long periods of traffic jams. One more aspect of Jensen's patent is direction finding where he utilizes differential discriminator technique similar to the one taught by Kyle in U.S. Pat. No. 4,591,834. The differential amplifier detects the difference between the signals from two oppositely directed microphones. That is the output voltage is then given by EQU V=G(S.sub.1 -S.sub.2)
if S.sub.1 -S.sub.2 &gt;.delta. and EQU V=0
if S.sub.1 -S.sub.2 .ltoreq..delta.
The advantage of this technique is that it cancels the effect of common noise. The disadvantage is that if the siren sound level is equal at both the sensors, example the emergency vehicle is very close, the system might fail to give any indication of its presence. A common disadvantage of all the prior art is that if the noise level is higher along one direction it can jam and confuse not only the direction determination capability, but the signal detection and the discrimination ability.